Alternative Centaurs?

[zen]

the heart of the Centaur class carriers is the use of two capital ship plants, producing 76,000shpin total.

Hermes got improved plants for 80,000shp.

If the RN had driven more powerful plant machinery prior to WWII, then arguably the Centaurs would be larger carriers.
Ideally to something like the postwar Y300 of between 45,000shp to 50,000shp.

Results on wartime design would presumably be just longer ships. Giving more hangar and flight deck area.

Consequently these ships would be more attractive for fast jets later on.....

 

[SSgtC]

It's a pretty easy change in the grand scheme of things actually. Have the RN be less resistant to adopting high pressure boilers and turbines. I'm not entirely sure what pressure the boilers in the Centaur class operated at, but if they were the standard 300 PSI that the RN adopted during the interwar period, they could have achieved a massive increase in hull size by using boilers similar to the ones used in the Essex class, which operated at 565 PSI. That would easily allow a larger hull with no additional machinery needed.

As a side note, it's amazing to me how the RN went from arguably the world leader in Naval Aviation before WWII, to making seemingly every wrong decision about naval aviation after the war.

 

[zen]

What changes.....

Well the obvious is that Hermes would carry more aircraft and this be of more use. Admiralty might then view rebuilding the other Centaurs to this standard.
It might even be attractive to modernise Centaur rather than Victorious, which in turn ought to be faster and cheaper....or even just run off more Centaurs to Hermes standard.

It also makes the lower end Medium Fleet Carrier more a continuation of the Hermes.

Will crunch some numbers to see if this works at all.

 

[zen]

Ok first rough draught.

DNC submitted a sketch design 29 May 1943.
Board saw these as supplements to future Armoured Carriers, and feared they were too expensive and complex. Controller ordered design developed despite lack of Cabinet approval. 12 July '43.
Resubmitted design Jan '44.
Formal approval Feb, and Legend in March
New design in '47. Hanger length cut by second accelerator to 416ft instead of 536.

Arguably with say a potential for 50,000shp ship could grow to Ark Royal's
LWL: 725ft
BWL: 94ft
LOA: 77ft
Beam extreme: 112

In essence replicating a single hangar version of Ark Royal and providing a flight deck equal to the Audacious class.

During this '47 process the cost comparison ought to this reveal that modernised Centaurs to Hermes standard could deliver far more efficient airpower than reconstruction of Illustrious class carriers and consequently Hermes would be the prototype for a possible second tranche of Light Fleet Carriers. In effect the original plan for another 4.
However it's more likely to just carry on concurrent with the rebuild plans for Illustriouses and Implacables.
That said those plans take a knock with the state of Formidable in '49 and could be abandoned in '52 after realising the state of Victorious's boilers and machinery. If we add in an earlier realisation of said plant, then this AH really takes hold in '49.

This concept would grow profoundly in '53 as studies would show that with an Angled Deck, such carriers could replicate the capability of larger and more expensive carriers of earlier. Redesign in '54 after New displacement limit approved 13 May. Possibly 28,500tons.
'57 projected air compliment 21 Sea Vixen and Scimitar, 8 ASW helicopters, 4 Skyraider or Gannet AEW, 2 SAR helicopters.

Concurrent 1950-1952 CV start of process followes OTL but hits transition in '54 Medium Fleet concept. This improving fast air from 21-29 to 24-32 depending on focus for ASW or Strike.
Hermes now formally prototyping lead for new class technologies.
Next generation ships aiming for aircraft weights of 50,000lb, revised to limit of 60,000lb after '57.

Cruiser-Carrier Hybrid starting '56 aiming to reuse Medium Fleet Hull and propulsion. By this time it's possible that new ships might already be under construction. Killed off after SPDC meeting in '58 and dropped from plans in 1960.

New CVA-01 process kicking off under same SPDC meeting will hit OTL process, but critically arrival of USN F4 and performance of F8 suggestes a 'Second Tier' capability sufficient to see of limited raids such as proxy forces might be able to assemble with Soviet 'advisors'. EoS mission can be done by this CV with F4 deep into 1970's. While Strike North can be effected with USN if Centaurs are upgraded or replaced with Light Medium Fleet.
Making replacement of first class Audacious ships less imperative.
P1154 only consolidates this view. Civil Lord will advocate continuation of plan.

Even with abandonment of CVA-01 process, either Light Medium Fleet or rebuild Centaurs offers cost effective provision compared to Audacious.

 

[Archibald]

During this '47 process the cost comparison ought to this reveal that modernised Centaurs to Hermes standard could deliver far more efficient airpower than reconstruction of Illustrious class carriers and consequently Hermes would be the prototype for a possible second tranche of Light Fleet Carriers. In effect the original plan for another 4.

Bingo. Is that OTL ?
I understand that Centaurs were considered LIGHT ESCORT carriers like the Colossus;
and that the Illustrious / Implacables were HEAVIES like Audacious;
BUT as far as upgrades to modern jets went...
Hermes completely bet the crap of Victorious !!! Surely enough that's paradoxical because Centaurs were 22000 tons hence LIGHT when Illustrious were 33000 tons + thus heavies...

We have to wonder, what's the better bargain to upgrade ?
Four Centaurs or the six Illustrious / Implacables ?

 

[zen]

During this '47 process the cost comparison ought to this reveal that modernised Centaurs to Hermes standard could deliver far more efficient airpower than reconstruction of Illustrious class carriers and consequently Hermes would be the prototype for a possible second tranche of Light Fleet Carriers. In effect the original plan for another 4.

Bingo. Is that OTL ?
I understand that Centaurs were considered LIGHT ESCORT carriers like the Colossus;
and that the Illustrious / Implacables were HEAVIES like Audacious;
BUT as far as upgrades to modern jets went...
Hermes completely bet the crap of Victorious !!! Surely enough that's paradoxical because Centaurs were 22000 tons hence LIGHT when Illustrious were 33000 tons + thus heavies...

We have to wonder, what's the better bargain to upgrade ?
Four Centaurs or the six Illustrious / Implacables ?

I'd go further and say if only as per this AH the Centaurs were a bit bigger and took more aircraft, then it would be cheaper to scrap the Illustrious class, recycle the metal and build that second tranche of Centaurs to Hermes standard or better.

Here's the kicker, Hermes had more Aviation Fuel than the Illustrious, Implacable or Ark Royal. More in fact than the other Centaurs.
Only the 1952, the Medium Fleet Carrier studies and CVA-01 had more Aviation Fuel.

 

[EwenS]

In relation to aviation fuel we need to have some context. At least four things changed between 1936 and 1959 concerning aviation fuel for carrier aircraft:-

1. A 1950s jet fighter around which Hermes was redesigned uses a lot more fuel than a Swordfish.
2. Numbers of aircraft carried increased to start with from 36 in Illustrious to a planned 100+ in the Malta before falling back as physical size and complexity began to take over. This was also affected by increasing use of deck parks during WW2.
3. Aircraft were operated at increasingly higher sortie rates
4. Perhaps most importantly, the fuel itself changed from highly inflammable petrol / avgas which required protected storage, generally behind armour, just like bombs, to Avcat which could be safely stored in the ships fuel tanks without protection. That allowed more aviation fuel to be carried but at a cost in the range of the ship. Petrol / avgas was required until the early 1960s when helicopters finally became turbine powered.

So the progression is as follows with service entry dates:-

Illustrious 1940 50,600 gallons of petrol.
Indomitable 1941 75,400 gal
Implacable 1944 96,230 gal
Colossus 1944 80,000 gal
Eagle as designed in 1942 115,000 gal petrol; as redesigned in 1946 and completed 1951 103,000 gal avgas 279,000 gal avcat. Her oil fuel load by comparison fell by 1,000-1,500 tons. Mix gradually reduced the avgas in favour of avcat over her life.
Malta 190,000 gal
Centaur as designed 1943 80,000 gal; as redesigned in 1947 and completed in 1953 50,000 gal avgas 295,000 Avcat. Carrying Avcat reduced the ships oil fuel load by some 300-400 tons
1952 carrier 450,000 gal avtur and 50,000 gal of avgas.
Victorious as reconstructed 1958 279,000gal Avcat plus 60,000 gal avgas.
Hermes 1959 330,000 gal Avcat plus 40,500 gal avgas
Eagle as reconstructed 1963 487,480 gal avcat. Her oil fuel load fell by another 2,200 tons compared with 1951.
CVA01 600,000 gal avcat
Ark Royal 1969 522,000 gal avcat. Not quite sure how it was done but she managed to retain the same oil fuel load as Eagle before modernisation despite shipping even more Avcat.
Invincible 1979 250,000 gal avcat.

 

[Hood]

I don't think there was much wrong with the basic Centaur design. It's just that the post-war lean years delayed their completion and by the time they did, carriers and aviation had moved on a long way. No-one in 1943 could foresee the Phantom in 1954, so its a little unfair to expect miracles from what was meant as a light fleet carrier for backing up the main fleet and escort duties.

 

[JFC Fuller]

For someone with a lot of time on their hands a deep review of the Victorious reconstruction costs based on the documents held at Kew and elsewhere would be a very interesting exercise for the small constituency of people who care. Especially if combined with similar work on other RN carrier programmes at the time. It is certainly true that she suffered almost uniquely from inept cost estimating combined with frequent scope changes and the effects of inflation. The result though, was a notably superior ship to Hermes at a claimed cost of over £30 million according D.K. Browne and George Moore (and repeated by Hobbes), or "nearly £20 million" according to the then Civil Lord of the Admiralty in 1959. Whats £10 million between friends in the 1950s?

Something else worth getting more detail on is what happened to Eagle, apparently it was an £11 million reconstruction that was chosen for her in the late 1950s but when she emerged in 1964 it was stated that £31 million had been spent on her reconstruction.

It was stated in Parliament that Hermes cost £18 million to build with a further £1 million worth of electronics on top of that, the electronics figure is the same as that given for the very similarly equipped Victorious so that at least makes sense. The £18 million though may have been a product of much of the labour and materials for her having been purchased at much lower wartime prices than those for the Victorious reconstruction.

The point of all the above is, I have absolutely no faith that the RN's cost estimates for its 1950s new-build carrier designs (£26 million for the 1952 carrier and £18 million for the 1954 medium carrier) were even remotely credible. Had either been built I suspect they would have come out significantly more expensive than either of those estimates. Similarly, had Implacable and Indefatigable both been given reconstructions to the Victorious standard, albeit with the process incorporating the lessons learned in the Victorious programme (e.g. no disassembling a new flight deck because of a belated realisation that new boilers were needed, a fixed initial scope, etc.) two excellent ships could have been produced for what may have been reasonable sums of money.

To conclude, the rebuild of Victorious took a painfully long time and greatly exceeded multiple cost estimates but ultimately produced an excellent ship. However, what we don't really know is whether the reconstruction was good value for money compared to building a new ship as it is entirely plausible that RN cost estimating for new build carriers was just as inaccurate as it was for rebuilding old ones. And we can't even be sure exactly what the Victorious rebuild cost.

 

[Archibald]

JFC : thanks for your hindsight.
While an impressive carrier, post-rebuild
I can still see two issues with Victorious
- only 24 aircraft
- only 10 years of service or even less
Too little after such a complex rebuild...

 

[JFC Fuller]

Had she been allowed, Victorious would have served for at least 13 years following her reconstruction, prior to her withdrawal it was intended that she would have one final commission that would have taken her to 1971.

Her air wing, with Sea Vixens, Buccaneers, Gannets and helicopters was more like 30+ and was larger than that of Hermes.

Unlike Hermes she had armour, 3" guns for self-defence and a 48 rather than 32 track CDS system. Additionally, she didn't have Hermes' forward deck edge lift that was unusable in higher sea states and she was a faster ship.

 

[EwenS]

David Hobbs published an article in Warship 2020 about the reconstruction of Victorious. Sadly it concentrated on the technical aspects of the reconstruction and didn’t delve into the real mysteries of the boiler debacle and cost increases as i’d hoped.

On the cost front he merely notes that “the steelwork of the hull’s fabrication amounted to little more than 20% of the total build cost, the greater part of the balance being spent on command, control and communication systems together with other sophisticated electronics, machinery, workshops and weapons test facilities which would have been just as necessary in a smaller hull.” That sounds a bit more than £1m to me.

Now given that those same facilities had to be built into Hermes, the difference in cost makes little sense. You may be right about the Hermes build cost. My other thought is that the costs for Victorious included development costs as first of type for all the electronics etc.

Reconstruction of the Implacables would have brought its own problems. The new hangar would have displaced workshops and accommodation from forward of the existing lower hangar, only part of which could be recovered aft. Probably as well that the Admiralty scrapped the idea in the end.

 

[zen]

JFC Fuller, and EwanS
Excellent points made there.

Victorious couldn't have deck edge lifts because she had just 14ft freeboard to the hangar deck. When 24ft was viewed as the safe minimum.
Compensation was the gaining of a full gallery deck, which was enormously successful.

But inboard lifts are inherently more weatherproof.

Sadly Illustrious and Formidable were not similarly updated. For Formidable, this was down to her material state, presumably Illustrious having been worked hard through the War was in poor state as well?

But Indomitable and Indefatigable were not ideal for reconstruction, as the efforts to design such proved.

Despite the increased aircraft compliment, it does raise a hindsight question over the two carriers.

 

[JFC Fuller]

On the cost front he merely notes that “the steelwork of the hull’s fabrication amounted to little more than 20% of the total build cost, the greater part of the balance being spent on command, control and communication systems together with other sophisticated electronics, machinery, workshops and weapons test facilities which would have been just as necessary in a smaller hull.” That sounds a bit more than £1m to me.

Now given that those same facilities had to be built into Hermes, the difference in cost makes little sense. You may be right about the Hermes build cost. My other thought is that the costs for Victorious included development costs as first of type for all the electronics etc.

We are in agreement, that is what I was getting at. An awful lot of glib remarks have been made across the internet and in various books about the relative value for money extracted from various RN carrier rebuilds compared to potential new-build ships. However, not enough is actually known about the given figures to actually make any credible judgement. For instance, the £1 million figure may cover Type 984, CDS and a few radios whereas the statement from Hobbs you referenced seems to cover everything, including boilers, weapons test facilities, onboard machine tools, etc, etc.

Reconstruction of the Implacables would have brought its own problems. The new hangar would have displaced workshops and accommodation from forward of the existing lower hangar, only part of which could be recovered aft. Probably as well that the Admiralty scrapped the idea in the end.

The Implacable/Indefatigable rebuild was to include stripping the ship down to the lower hangar deck then rebuilding with a 17ft 6" hangar (at least) and a gallery deck above that, as in Victorious. That enough space could be found in Victorious for the required workshops and accommodation suggests it should have been possible to find it on the longer Implacable hull, though obviously original drawings would be good to see if any were ever produced.

 

[_Del_]

Refit costs, much like construction, can be notoriously difficult to project. I recall talking to a docent at the Midway museum who told me about the angled deck refit. Congress was concerned about the rising costs of nuclear carrier builds, so the ship got (among other goodies), something like 40% more deck space to make her fit to handle larger aircraft (E-2, TFX, etc). Ended up with a higher angle of offset to clear the cats. Costs were well over twice what was expected and started becoming unwelcomingly comparable to the nuclear new builds while significantly less capable.

I don't mean to dispute anything you said about the relative merits one way or another (indeed, I don't pretend to know enough to), just that projected costs for either option are, or at minimum can be, misleading.

 

[zen]

Rereading the tortuous convolutions gone through to get improvements on Implacable. I'd say it wasn't worth it.
It was virtually a new design compared to Victorious. A totally new set of compromises had to be agreed and never could.
The hard reality is the most expensive and longest to achieve element was the new hangar and flight deck.
Irrespective of electronics fit, fuel storage, lifts etc...
The full gallery deck was cut as to make it work meant lowering the ceiling by 6", not only cramping the deck but making the flush depression of guns even more difficult. But cutting the gallery deck meant expanding the island to accommodate enough space. Which in turn proved unacceptable.
The fact is Implacable and Indomitable, were expedient WWII solutions, not ideal for post war solutions after 1956.

 

[EwenS]

The Implacable/Indefatigable rebuild was to include stripping the ship down to the lower hangar deck then rebuilding with a 17ft 6" hangar (at least) and a gallery deck above that, as in Victorious. That enough space could be found in Victorious for the required workshops and accommodation suggests it should have been possible to find it on the longer Implacable hull, though obviously original drawings would be good to see if any were ever produced.

I agree that that the books all say the plan was to strip her down to the lower hangar deck. From that the deduction seems to be that the floor of the lower hangar would form the basis of a new extended 17’6” hangar. But when you look at the inboard profile of Victorious and Implacable there is a significant difference.

In Victorious the hangar deck is at the level of the quarterdeck. Under it are the Upper Deck and the Main Deck. Immediately under the Main Deck are the boiler rooms and engine rooms. Amidships, the space, two decks deep between the boiler room and the hangar deck is taken up with boiler room fans and vents and uptakes carrying the exhaust gases across the ship to the funnel. The space aft of those uptakes, and above the engine rooms, under the hangar deck is filled with workshops and accommodation. This can be seen in the various drawings in the Anatomy of the Ship book on Victorious.

There is a diagram of the inboard profile of Implacable as completed in Friedman’s British Carrier Aviation. The most noticeable thing is that the lower hangar deck is NOT at the level of the quarterdeck as in Victorious. It is one deck lower. That leaves only one deck space between the lower hangar deck and the engine room for workshops and accomodation. The forward end of the lower hangar is in line with the aft end of the boiler rooms. Between the deckhead of the boiler room and the floor of the UPPER hangar are 3 deck spaces. The cross section diagram shows the lowest of these contains the boiler fan spaces. Given the layout in Victorious at least one more deck level must contain the cross ship uptakes.

So in any reconstruction, in order to achieve a full length hangar clear of the boiler uptakes, it seems to me that the floor of the lower hangar must be raised by one deck, to the level of the quarterdeck. That creates a vacant space under the new hangar floor that I referred to previously. BUT the forward extension of the new hangar then removes two decks worth of space forward of the boiler uptakes.

I came to realise the true position of Implacable’s lower hangar while trying to reconcile the hull depths of an Illustrious v Indomitable v Implacable. The starting point for the Implacable design was a modified Illustrious hull and layout.

Detailed deck plans of Indefatigable are available from the NMM but at c£140 for each deck it is a bit rich for my taste.

 

[Hood]

I think JFC Fuller makes an excellent point regarding costs estimations for rebuilds.

It's clear that some aspects of Victorious' rebuild were bungled (having to re-open her up for boiler access etc.), but some of the cost increases would have been inevitable with inflation plus the development costs of the electronics etc. (presumably Type 984 and CDS amortisation would have been spread through fewer ships than planned). There is also the possibility that the 'Whitehall warriors' inflated the cost effectiveness claims of new-build carriers over reconstructions to ger shiny new boats to play with, and that these myths have entered the story.

We must also consider that the Admiralty/MoS had relatively little experience to go on when it came to cost estimates for major reconstructions. The battleship reconstruction programme had been twenty years earlier and did not resort to the kinds of major hull rebuilding being planned for the carriers. Most of the battleship changes were replacement of machinery, boilers, superstructures and some bulging and adding armour, not cutting ships down and rebuilding their framing and moving decks around. Post-war there were no other reconstructions on this scale, ships under construction (carriers and cruisers) did receive lengthy work but their build times were interrupted and lengthened by decades in some cases and their overall costs can't have been impressive.

Hermes may well have cost less because less work needed to be done. Construction begun in July 1944 and stopped in 1945 but it only took a year to get her to launching condition in 1952-53 which suggests she must have been fairly well along when construction was halted and materials may have been on hand, British Steel would have supplied the rest and fairly cheap prices.. So most of the material costs in steel etc. would have been expended by 1952. That just leaves the completion and fitting out and modifications, its a lot easier to adapt an unfinished ship as less stripping out would be required.

Hobbs states that 80% of Victorious costs were on things other than the structural elements, that leaves us with £24.8M.
The electronics for Hermes are stated as having only cost £1M (though that's a vague term and could cover anything, just radar, just comms, just wiring?) Victorious had a similar outfit but updated in some areas, even so 32-track CDS probably would not have cost vastly more, so lets say the total cost is £1.5M or even £2M on the safe side. R&D costs might have come into play but I would have expected them to be amortised across the production batch of Type 984s and CDS systems, installation costs might have been higher though.
Victorious's 3in guns were supplied under MDAP so that cost is covered.
So where did the other £22.8M go?
Reboilering (Foster-Wheeler means imports and all that implies with currency exchange and balance of payments, plus - I could be wrong - no other RN ships then had Foster-Wheeler boilers so that implies additional training and equipment), steam catapults, weapons test facilities, new workshops and equipment (though presumably these would have been standard workshop kit and tools being ordered for other carriers), finally you have labour costs plus the delays and having to undo and redo previous work. None of this is cheap but its hard to see all this eating up over £22M.
Its interesting that Hermes' airgroup was costed at £20M, I wonder if some of the airgroup cost was attributed within the cost breakdown?

I would agree that any new construction cost would be inflated in reality, though it could be argued the costing teams had more exeprience with new-builds, the estimates can only really be considered as lower limits, its hard to imagine them being as cheap as a reconstruction or cheaper than the half-built WW2 generation whose costs had already been partially sunk into wartime funding.

 

[zen]

Victorious's 3" guns were the only mounts of that US source, a host of issues made purchase of more very difficult. Make them a one off in the fleet and likely to be replaced by domestic 3"/L.70 later on in planning.

 

[zen]

What if....at least the two of the second tranche of Centaurs had not been cancelled and scrapped?
Hermes and Arrogant?

Had these been completed to Elephant standard....?

 

[EwenS]

I would disagree about your analysis of the BB reconstructions in the 1930s. The 4 biggest rebuilds (Warspite, QE, Valiant & Renown) saw the hulls stripped back to the main deck, old machinery ripped out and the machinery spaces completely reconfigured and new superstructures built. The new more efficient and lighter machinery occupied less space which could then be used for other purposes. 24 boilers reduced to 8 for example.

What did change between the 1930s and 1950s was the need for a huge increase in electrical output and and the need for so much more wiring for radars, powered gun mounts etc. So the nature of much of the work changed if not its extent. During WW2 electricians were in short supply. Not sure if it was any better by 1950.

While Wiki says work restarted in 1952, McCart’s history of Hermes has work authorised to restart on her in 1949. A 3 year delay before starting any work at all seems odd. As I noted a further delay came from a decision to fit steam catapults. I also have a note that she was delayed by work of Majestic (HMAS Melbourne) completing in the same yard, but that work didnt finish until 1955. The final redesign took place after she launched and that included the angled deck and the side lift, so some stripping back would have been required.

 

[EwenS]

What if....at least the two of the second tranche of Centaurs had not been cancelled and scrapped?
Hermes and Arrogant?

Had these been completed to Elephant standard....?

The second tranche of Centaurs never got beyond an order.

There were big arguments about these 1943 light carriers, even before they were ordered. The First Lord of the Admiralty didn’t want them while the First Sea Lord and his Deputy did as they perceived a need for a new generation of carriers to operate a new generation of aircraft in about 1947/48 which couldn’t be handled by existing ships. So while all 8 were ordered in July/Aug 1943 the argument went on and a compromise was reached by late in 1943 and construction of only 4 was authorised to proceed. There was a bit of chopping and changing in early 1944 as to exactly which ships were to be built but eventually Centaur, Albion and Elephant were laid down between March & June 1944. The 4th ship was to be Monmouth at that stage but Fairfield’s were having capacity problems and couldn’t move it forward. Then in early 1945 Bulwark replaced Monmouth in the plan and was laid down in May on the slip next to Centaur with accumulated materials being passed from Fairfield to Harland & Wolff to expedite the build.

Then in the first post-war round of cuts the 4 ships that still existed only on paper were axed. Those were Hermes, Arrogant, Monmouth and Polyphemus. That freed up the Hermes name for transfer to Elephant over at Cammell Laird. At that point the First Lord’s veto on construction of more than 4 was still in place so it was probably one of the easier decisions to make. The yards at that stage were only holding a minimal amount of materials for them, gathered before suspension was put in place in 1943.

So to get any more of this class you would have to go back and refight the battles of 1943, not just those of 1945. And any build would be starting from scratch.

 

[zen]

I thought at least one was actually scrapped, so something had started.

Anyway on the basis of the AH said decisions in '43 might have been different.

 

[Archibald]

Considering how hopeless the Ill-dom-able (Ill-doom-unable ?) seem to have been, more Centaurs & Audacious get my vote. Heck, Maltas would be fine (or maybe not, they weren't perfect by any mean, plus they were still paper projects by 1946).

 

[Archibald]

What if....at least the two of the second tranche of Centaurs had not been cancelled and scrapped?
Hermes and Arrogant?

Had these been completed to Elephant standard....?

The second tranche of Centaurs never got beyond an order.

There were big arguments about these 1943 light carriers, even before they were ordered. The First Lord of the Admiralty didn’t want them while the First Sea Lord and his Deputy did as they perceived a need for a new generation of carriers to operate a new generation of aircraft in about 1947/48 which couldn’t be handled by existing ships. So while all 8 were ordered in July/Aug 1943 the argument went on and a compromise was reached by late in 1943 and construction of only 4 was authorised to proceed. There was a bit of chopping and changing in early 1944 as to exactly which ships were to be built but eventually Centaur, Albion and Elephant were laid down between March & June 1944. The 4th ship was to be Monmouth at that stage but Fairfield’s were having capacity problems and couldn’t move it forward. Then in early 1945 Bulwark replaced Monmouth in the plan and was laid down in May on the slip next to Centaur with accumulated materials being passed from Fairfield to Harland & Wolff to expedite the build.

Then in the first post-war round of cuts the 4 ships that still existed only on paper were axed. Those were Hermes, Arrogant, Monmouth and Polyphemus. That freed up the Hermes name for transfer to Elephant over at Cammell Laird. At that point the First Lord’s veto on construction of more than 4 was still in place so it was probably one of the easier decisions to make. The yards at that stage were only holding a minimal amount of materials for them, gathered before suspension was put in place in 1943.

So to get any more of this class you would have to go back and refight the battles of 1943, not just those of 1945. And any build would be starting from scratch.

So let's stick with 4*Centaurs then, but get me that third Audacious or (even better) a couple of Maltas...

 

[zen]

So let's stick with 4*Centaurs then, but get me that third Audacious or (even better) a couple of Maltas...

I'd leave Malta alone and just complete that third Audacious.

 

[EwenS]

The original Eagle had only been laid down in Dec 1943 and had been severely delayed by the LST(3)/Transport Ferry programme which had a higher priority in 1944/45. VA (Tyne) were allocated 5 to build in Dec 1943 which were laid down between May and Oct 1944 with 3 completed in the second half of 1945.

The result was that Eagle was only 26% complete by Dec 1945 with £1.95 million having been spent on her. By that stage the need was to save money in the postwar world. Her cancellation was estimated to save £5.5 million. Only the cruiser programme cancellation (4 ships) saved more (£17.8 million)

 

[Archibald]

Thanks for the data ! Very useful. Context is everything.

 

[zen]

A further thought.

IF.....if plant development in the late 40's and 50's got over 60,000shp.
THEN....1952 CV could make do with 3 sets for 180,000shp.
AND Medium Fleet with just 2 sets for 120,000shp.
Resulting in ships with less volume taken by plant machinery with resulting costs reduced.
This would particularly tell on the Medium Fleet Carrier.
It seems the French achieved something like this.
Though the hanger height on the Clemenceaus is odd.

 

[orlovsky]

Only somewhat related to this topic, but does anyone have more information on the boilers used or planned in RN carriers?

The pressure was lower than those used by the US Navy, limiting the catapults. But the details are anecdotal at best.

HMAS Melbourne 400 psi:
"At Flying Stations, the pressure of the forward boilers was increased from the normal 400 psi to 430 psi, to allow the catapult steam accumulators to be charged."
( https://www.navyhistory.org.au/occasional-paper-4-hmas-melbourne-ii/ )

In Hobbs, there is a mention of 4000 psi for Ark or Eagle, but probably an error for 400. From the start, or installed in a refit?

The 1949 Daring class got Foster Wheeler boilers @ 650 psi. Were they planned for the 1952 carrier, too? I think no RN carrier used those.

What was the "2nd reboilering" of Victorious about? Did she get an "upgrade" to 400 psi, or more?

Hermes probably used the same as Ark/Eagle/Victorious/Melbourne?

What was planned for CVA-01?

Seems to be even more arcane than details for the steam catapults....

 

[EwenS]

In no particular order, other than that in which I can find the data, which is as you say hard to come by:

CVA01 - 6 boilers 1,000psi at 900 degrees F (482 degrees C) see Warship 2014 article “CVA-01: Portrait of a Missing Link”

Victorious as rebuilt in 1958 - 6 Foster Wheeler type boilers operating at 440psi see “Anatomy of the Ship The Aircraft Carrier Victorious”. I’m not aware of any machinery changes to her after that.

Ark Royal on completion - 400psi. No change noted in any of her later refits. From “Britain’s Greatest Warship HMS Ark Royal IV”

All the Colossus / Magnificent class would have completed with the same machinery, being a half set of that installed in the Fiji class cruisers. The Admiralty 3 drum boilers of the period all seem to have been around 400psi e.g. KGV class 380/410psi at 750 degrees F from Burt’ British Battleships. I also have a Warship article that notes the Battle class destroyers of 1942, when compared to the L class, would raise boiler pressures from 300psi to 400psi and steam temps from 660 degrees to 700 degrees.

If you want catapult details the best source I’ve found is “Farnborough and the Fleet Air Arm” by Geoffrey Cooper who used to work there.

 

[orlovsky]

Thank you, very interesting... so Victorious was unique in that regard. The data for her bs4 catapults may be related to that higher pressure.

The bs6 on CVA-01 is - as far as numbers are given - essentially as strong as the c-11, despite being ~40 ft longer and having higher pressure available. All very curious.

Hermes should also be in the 400 psi boiler ballpark. Here at around 15:40 steam pressure is reset from 350 psi for the scimitar to 310 psi for a Sea Vixen.

View: https://www.youtube.com/watch?v=tsE9oCdSEEI


I have “Farnborough and the Fleet Air Arm” seen mentionned, but not quoted with anything specific. Does it deal with the various bs4 and bs5 versions and the steam accumulators? Thanks again.

 

[EwenS]

The Farnborough book has an Appendix 6 detailing the "accelerators" installed on each British carrier from 1935 to 1978 and the specs of those devices. It doesn't give the steam pressures, just launch weights and end speeds and for the steam catapults the length so probably not what you seem to be looking for.

Don't forget that when launching an aircraft one limiting factor is the G forces applied to the airframe and crew. No point in using all that steam pressure to boost the aircraft, if the end result is that the crew black out on launch, the wings come off and the fuselage sails off into the briny for the carrier to run over it!

Look at some of the test work done on the new EMALS catapults on the USS Ford. For a while it couldn't launch Sea Hornets with drop tanks. https://news.usni.org/2017/07/28/em...-heaviest-airplanes-ford-class-carrier-launch

So the planned BS.6 (250 ft long) in CVA.01 could launch a 60,000lb aircraft at speeds up to 150 knots, or as a minimum 15,000lb at 110 knots, without exceeding 5G. That allowed the launch of unreheated Phantoms and Buccaneers and a margin for the prospect of heavier aircraft to come. While doing so it was intended that her speed capablity should not drop below 25 knots (from 28 knot max) through diversion of steam to the accumulators.

By way of comparison the C-13-1 & 2 catapults in the Nimitz class have a stroke of just over 306-310 feet and are capable of launching 80,000lb at 140 knots. They exert something like 4G initially dropping to 2G at the end of the run. And today's aircraft like the F-18E/F are actually lighter than the A-3 Skywarrior and F-14 Tomcat of the past. AIUI one of the advantages of nuclear power is that there is enough steam available to maintain speed while launching aircraft unlike in a traditional boiler powered carrier.

That is the fascinating thing about carrier aviation. There is a symbiotic relationship between the ship and its aircraft.

Edit:- The other think to remember is that in modern carrier aircraft all the force applied by the catapult shuttle passes into the airframe via the nosewheel leg and not cables connected to catapult points in the fuselage or wings.

 

[SSgtC]

AIUI one of the advantages of nuclear power is that there is enough steam available to maintain speed while launching aircraft unlike in a traditional boiler powered carrier.

Actually, no. The USN still deals with the Nimitz class losing speed as steam is diverted from propulsion to the cats. It's not as extreme as in some of the older ships (for example, an Essex class could normally do 31 knots at flank, but during flight operations the most it could do while still delivering full power cat shots was 19 knots) but it still happens. AFAIK, the Navy has never officially said how much speed they lose, but it's believed that they only drop from 30 knots to no less than 25.

 

[isayyo2]

AIUI one of the advantages of nuclear power is that there is enough steam available to maintain speed while launching aircraft unlike in a traditional boiler powered carrier.

Actually, no. The USN still deals with the Nimitz class losing speed as steam is diverted from propulsion to the cats. It's not as extreme as in some of the older ships (for example, an Essex class could normally do 31 knots at flank, but during flight operations the most it could do while still delivering full power cat shots was 19 knots) but it still happens. AFAIK, the Navy has never officially said how much speed they lose, but it's believed that they only drop from 30 knots to no less than 25.

Sounds like EMALS is worth the headache then

 

[orlovsky]

So the planned BS.6 (250 ft long) in CVA.01 could launch a 60,000lb aircraft at speeds up to 150 knots, or as a minimum 15,000lb at 110 knots, without exceeding 5G. That allowed the launch of unreheated Phantoms and Buccaneers and a margin for the prospect of heavier aircraft to come. While doing so it was intended that her speed capablity should not drop below 25 knots (from 28 knot max) through diversion of steam to the accumulators.

The appendix still sounds interesting, maybe I'll order the book.

Is the bs6 nr from that appendix? Hobbs has the bs6 at 115 kts for 55k lbs (which is little), and the initial C-13 (which should be comparable) managed ~135 kts for 60k lbs at 1000 psi. The 150 kts may include 20-25 kts wind over deck?

What you can actually launch with the capacity is another matter, yes. If the catapult breaks the plane or the pilot, well...

 

[SSgtC]

Sounds like EMALS is worth the headache then

Pretty much yeah. That's one of the biggest attractions for it. No loss of speed, which means more wind over the deck which means you have a bigger envelope in which to launch aircraft (at both the high end and low end)

 

[EwenS]

So the planned BS.6 (250 ft long) in CVA.01 could launch a 60,000lb aircraft at speeds up to 150 knots, or as a minimum 15,000lb at 110 knots, without exceeding 5G. That allowed the launch of unreheated Phantoms and Buccaneers and a margin for the prospect of heavier aircraft to come. While doing so it was intended that her speed capablity should not drop below 25 knots (from 28 knot max) through diversion of steam to the accumulators.

The appendix still sounds interesting, maybe I'll order the book.

Is the bs6 nr from that appendix? Hobbs has the bs6 at 115 kts for 55k lbs (which is little), and the initial C-13 (which should be comparable) managed ~135 kts for 60k lbs at 1000 psi. The 150 kts may include 20-25 kts wind over deck?

What you can actually launch with the capacity is another matter, yes. If the catapult breaks the plane or the pilot, well...

BS6 data was from the Warship article I referred to above not the Farnborough book.

AIUI the catapult end speeds are all without any wind over the deck.

 

[EwenS]

Sounds like EMALS is worth the headache then

Pretty much yeah. That's one of the biggest attractions for it. No loss of speed, which means more wind over the deck which means you have a bigger envelope in which to launch aircraft (at both the high end and low end)

And that confuses me. You still have to generate the electricity to power the EMALS which comes from the steam produced by the nuclear power plant. Maybe just degrades a bit more gracefully?

 

[isayyo2]

Sounds like EMALS is worth the headache then

Pretty much yeah. That's one of the biggest attractions for it. No loss of speed, which means more wind over the deck which means you have a bigger envelope in which to launch aircraft (at both the high end and low end)

And that confuses me. You still have to generate the electricity to power the EMALS which comes from the steam produced by the nuclear power plant. Maybe just degrades a bit more gracefully?

When the catapult is "shot" the steam used is expended and lost, continually requiring new steam from the turbines.
With EMALS, the only steam being generated is in the boilers down below; maybe some steam is still being used for laundry and dish washing.